Reference is made to copending U.S. patent application Ser. No. 555,863 and Ser. No. 555,864.
The present invention relates to a color television (TV) imaging apparatus of the type using an imaging device with a photoelectric transducer section in which a color separation stripe filter capable of generating a multiplex color TV video signal is disposed. More particularly, the present invention is concerned with an apparatus for applying bias light to the imaging device.
A modern color TV camera employs a color TV imaging device in which a color separation stripe filter is disposed in a photoelectric transducer section to generate multiplex color TV video signals. Typical of such color TV cameras is a single tube type color TV camera which uses as its imaging device an image tube having a photoelectric transducer section with a color separation stripe filter on a faceplate, or a single plate type color TV camera whose imaging device is a solid state image sensor having a photoelectric transducer section with a color separation stripe filter. Because such types of TV cameras are easy to produce in a simple, compact and light-weight construction, various types of products with such capabilities are now in the market.
As well known in the art, undesirable afterimage develops in a color TV camera of the type including in a photoelectric transducer section thereof a photoconductive film which shows a photoelectric phenomenon, a kind of internal photoelectric effects. An expedient heretofore employed to reduce afterimage in such an imaging device is applying bias light in an even distribution to the entire surface of the transducer section. Various methods have been proposed for the application of bias light to the imaging device such as (1) building a light source in a lens to apply bias light to the whole transducer surface, (2) locating an annular light source in the vicinity of the transducer section to apply bias light to the whole surface of the latter, and (3) guiding light from a light source located at the rear of the transducer section to the whole transducer surface by utilizing the wall of the image tube or forming a light inlet opening in an electrode of the image tube.
The prior art methods for the supply of even bias light to the entire transducer surface described above commonly employ scattered light, so that the appearance of afterimage may be suppressed while eliminating shading.
The supply of bias light for reducing afterimage is similarly applicable to a color TV imaging device of the type having a photoelectric transducer section which is equipped with a color separation stripe filter for generating a multiplex color TV video signal.
When applied to a color TV imaging device, the prior art bias light supply means discussed as three different methods (1) to (3) are successful to effectively reduce afterimage in the transducer section by applying bias light thereto. However, all the three methods are not fully acceptable in one respect or another. The method (1) fails to offer interchangeability between lenses, the method (2) involves difficulty in reconciling quantity and even distribution of light, and the method (3) is incapable of supplying a sufficient quantity of light.
Another problem encountered with a color TV camera furnished with an imaging device of the type described is that colors in a scene cannot be reproduced with good reproducibility when the scene is dark. While various implementations have been proposed against such poor color reproducibility in dark scenes, we have found that the problem can be solved by processing the bias light in a special manner, as disclosed in Japanese Utility Model Application No. 57-124681 (Japanese Unexamined Utility Model Publication No. 59-29878). The solution we found is to apply bias light which is parallel to a plane defined by an extending direction of an array of stripes in the stripe filter and a direction perpendicular to the surface of the transducer section, using a reflector plate having a parabolic configuration. Utilizing this technique, we readily attained a color TV camera which features favorable color reproducibility even in dark scenes. The theme of our farther study, therefore, has been to embody the above-described technique and develop a bias light supply device which features high productivity and ability for general purpose application.